Not exactly a resolution, but I made some changes to the pond.... Fenced off 2/3 for the koi, and the remaining 1/3 for lilies. With the koi away from the plants, I can keep the cover off that end, so you can see the lilies much better. I also reduced the number and size of plants in the middle of the pond, giving a sleeker, less cluttered appearance. And when the few that I kept started getting overgrown, I did keep my promise to divide them, in order to keep the more tidy look.